1. Field of the Invention
The present invention relates to an electromagnetic device, and in particular to an improved electromagnetic device having a magnetic circuit with good magnetic efficiency.
2. Discussion of the Related Art
An example of a conventional electromagnetic relay is disclosed in the Japanese Laid-open Publication No. Sho 61-218025, a magnetic circuit of which is shown in FIGS. 14 to 16 for the convenience of explanation.
The conventional electromagnetic device includes a roughly U-shaped iron core 2 wound with a coil 1, a permanent magnet 3 fixing both internal ends of the core 2 in a position near and walls 2a and 2b thereof, and a front view roughly T-shaped armsture 4 pivotally supported on a central portion of an upper surface of the permanent magnet 3 for alternately contacting and walls 2a and 2b of the core 2.
When the electromagnetic device is not excited, one end 4a of the armature 4 is attracted by one end 2a of the core 2. When a voltage is applied to the coil 1 so as to produce a magnetic flux canceling a magnetic flux of the permanent magnet 3, the armature 4 swings clockwise against a magnetic force by the permanent magnet 3 so that other end 4b of armature 4 is attracted by other end wall 2b of the core 2. Even after the excitation of the relay is released, the armature 4 retains the attracted position by the magnetic force of the permanent magnet 3.
The attracting force characteristic of the conventional electromagnetic device is influenced by the magnetic flux of the permanent magnet 3 flowing through a winding center of coil 1, but roughly only a half of the magnetic flux produced by the permanent magnet 3 flows into the core 2. Accordingly, roughly only a half of magnetic energy of the permanent magnet 3 is utilized for operation of this device, resulting in a low magnetic efficiency.